An epidemiologic analysis of co-occurring alcohol and tobacco use and disorders: findings from the National Epidemiologic Survey on Alcohol and Related Conditions.

The 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions (NESARC) sought to determine the prevalence of drinking, smoking, and associated disorders in the general population. This survey, which includes a large representative sample of the adult population of the United States, found that drinking rates were highest among young adults and declined with increasing age. Rates of smoking and co-use of alcohol and tobacco were highest among the youngest respondents and declined thereafter. Similar patterns existed for the presence of alcohol use disorders (AUDs), nicotine dependence, and comorbidity between AUDs and nicotine dependence. Among ethnic/racial groups evaluated, Whites were most likely to drink and Native Americans/Alaskan Natives were most likely to smoke and to have an AUD, nicotine dependence, or comorbid AUD and nicotine dependence. Finally, the rates of tobacco use, daily tobacco use, and nicotine dependence increased with increasing levels of alcohol consumption and the presence of an AUD. These findings have important implications for the development of prevention and intervention approaches.

N umerous studies have demonstrated that excessive alcohol consumption and tobacco use are independently associated with a plethora of health-related, social, and economic adverse consequences for the consumers of these legal substances as well as for society at large (Centers for Disease Control and Prevention [CDC] 2004[CDC] , 2005a)).Some of these detrimental effects can be exacerbated in people who use and abuse both substances.For example, the risk of certain cancers is greater for people who drink and smoke than for people who use only one of these substances (National Institute on Alcohol Abuse and Alcoholism [NIAAA] 1998a).To prevent the harmful interaction of alcohol and tobacco use and ameliorate its impact on the individual and society, it is important to understand the mechanisms contributing to the use and abuse of both substances.Many studies into these mechanisms have identified brain molecules, such as neurotransmitters and nicotinic receptors, that interact with alcohol and/or nicotine and which mediate the effects of these substances on the brain.Similar analyses also have identified mechanisms that mediate sensitivity to alcohol and/ or nicotine, as well as the rewarding properties of the two drugs.(For more information on these mechanisms, see the articles by Funk and colleagues, Davis and de Fiebre, and Grucza and Bierut in this issue.) Another large area of research is concerned with how the use of or dependence on one of these substances affects the treatment outcome for dependence on the other substance.For example, studies have begun to address the fol lowing questions: Are alcohol-dependent patients who are also nicotine depen dent less likely to have successful alco holism treatment outcomes than those patients who are not nicotine dependent?Should both dependencies be treated at the same time or consecutively?And are special treatment approaches needed for patients who are dependent on both rather than just one substance?This research already has yielded valuable insights.(For more information, see the articles by Foulds and colleagues, Gulliver and colleagues, Ziedonis and colleagues, and Kodl and colleagues in this issue.) Although all of these avenues of research are of the utmost importance, it is equally critical to obtain a solid under standing of the scope of the problem.Thus, it is important to know the rates of alcohol and tobacco use and co-use in the general population and whether certain demographic subgroups are particularly at risk of using both alcohol and tobacco or being dependent on both substances.Studies of this nature are rare in the literature.In a previous issue of Alcohol Research & Health, Anthony and Echeagaray-Wagner (2000) presented an epidemiologic analysis of alcohol and tobacco use and co-use using national data collected before 1997.This analysis found that the prevalence of co-occurring alcohol and tobacco use and disorders was lowest among young adolescents, peaked among young adults, and declined thereafter.The peak rate of alcohol and tobacco co-use among young adults ranged from 35 to 45 percent, and the peak rate of co-dependence was approximately 10 percent.
In addition to determining the prevalence of co-occurring alcohol and tobacco use and disorders in the general population and for certain demographic subgroups, it is important to understand how rates of tobacco use and nicotine dependence vary among people with different characteristics of alcohol con sumption.Over the last 20 years or more, accumulating evidence has indeed pointed to a dose-response relationship between alcohol and tobacco use: • Dawson (2000) reported that peo ple who abuse or are dependent on alcohol are more likely to use tobacco and are heavier users than people who abstain from alcohol.
• DiFranza and Guerrera (1990) found that 83 percent of alcoholics were smokers, compared with 34 percent of nonalcoholics.
• Bobo and Husten (2000) showed that 37 percent of adults who were classified as current drinkers were also current smokers, compared with 13 percent of abstainers.
• Other analyses indicated that smoking rates and the number of cigarettes smoked increase with increasing alcohol consumption (e.g., Friedman et al. 1991).
Although data such as these strongly point to an association between drinking and smoking, the existing studies often have characteristics that, while making them useful for addressing specific research questions, limit their generaliz ability to the general population.These characteristics include the use of treatment samples, local community samples, or special subpopulation samples rather than nationally representative samples.Moreover, most comorbidity studies focused on smoking or cigarette smok ing as the measure of tobacco use (e.g., Dawson 2000;Anthony and Echeagaray-Wagner 2000;Friedman et al. 1991), ignoring other modalities of tobacco use (e.g., the use of snuff and chewing tobacco).In addition, many of the existing studies were based on surveys conducted in the 1980s and have used diagnostic criteria that are no longer current.Particularly with the preva lence of tobacco use declining dramati cally in the United States in recent decades (Marks et al. 1997;CDC 2005b), epidemiological studies based on current national data are needed to provide updated estimates of alcohol and tobacco co-use in the general population.
This article addresses these issues by updating the findings presented by Anthony and Echeagaray-Wagner (2000)

Data
The present study is based on data from the first wave of the NIAAA-sponsored NESARC, which was conducted in 2001-2002.NESARC is among the largest nationally representative comor bidity surveys ever conducted and includes extensive questions on alcohol and tobacco (as well as other substance) use and related disorders.The NESARC sample includes 43,093 respondents ages 18 and older, representing the civilian, noninstitutionalized adult population of the United States, includ ing residents of all 50 States and the District of Columbia.Military personnel living off base and persons living in noninstitutionalized group-quarter housing, such as boarding houses, shelters, and dormitories, also were included (Grant et al. 2003).The sampling frames for housing units and group-quarter units were derived from the Census 2000/ 2001 Supplementary Survey and the Census 2000 Group Quarters Inventory, respectively.NESARC oversampled Blacks, Hispanics, and young adults (ages 18-24) to allow for more reliable estimates of these groups.Data were col lected via face-to-face, computer-assisted interviews in household settings.From each household, one adult was selected for interview.The overall response rate for NESARC was 81 percent.

Measures
Alcohol Measures.All alcohol mea sures reflect consumption and diagnos tic status during the past year (i.e., the 12 months preceding the NESARC interview).Although NESARC col lected alcohol data separately for each of four beverage types (i.e., wine, beer, coolers, and distilled spirits), the results presented here are the aggregate across beverage types.The various alcohol measures are defined as follows: • Lifetime abstainer-Never had one or more drinks of alcohol during the course of a lifetime, excluding small tastes or sips.
• Former drinker-Had at least one drink prior to the past year but no drinks during the past year.
• Current drinker (or alcohol use)-Had at least one drink of alcohol during the past year.Based on pastyear consumption, current drinkers are divided into three drinking levels: -Light drinker-Had three or fewer drinks per week.
-Moderate drinker-Had 4-14 drinks per week for men and 4-7 drinks per week for women.
-Heavy drinker-Had more than 14 drinks per week for men and more than 7 drinks per week for women.
• Tobacco Measures.Like the alcohol measures above, the tobacco measures employed in the present study also reflect past-year use and diagnostic sta tus.NESARC collected data separately for each of four tobacco modalities (i.e., cigarettes, cigars, pipes, and snuff and chewing tobacco); however, the analyses presented here are an aggregate across all modalities.The various tobacco measures are defined as follows: • Tobacco use-Had smoked at least 100 cigarettes or 50 cigars, had smoked a pipe at least 50 times, or had used snuff or chewing tobacco at least 20 times during the course of a lifetime and had used any tobacco modality at least once during the past year.
• Daily tobacco use-Had used at least one tobacco modality at least once every day during the past year.
• Nicotine dependence 1 -Met at least three of the seven DSM-IV criteria for nicotine dependence in the past year.Similar to alcohol dependence, nicotine dependence was diagnosed using the AUDADIS-IV.The diag nostic criteria of nicotine dependence include tolerance, withdrawal syn drome or using tobacco to relieve/ avoid withdrawal symptoms, using tobacco more than intended, persis tent desire or unsuccessful attempts to cut down or stop tobacco use, great deal of time spent using tobacco, giving up activities in favor of tobacco use, and continued using tobacco despite physical or psycho logical problems caused by its use.Many of the specific symptom items used to operationalize nicotine dependence criteria are different from those for alcohol dependence (Grant et al. 2004).

Co-Occurrence of Alcohol and Tobacco Measures.
Based on past-year alcohol and tobacco use and disorder status, two measures are defined: • Co-use-Had used both alcohol and tobacco within the past year.
• Comorbidity-Had both an AUD and nicotine dependence in the past year.Men and women had similar rates of using alcohol only (44.4 and 43.2 percent, respectively) and using tobacco only (6.4 and 5.6 percent, respectively) (Figure 1a).However, men were much more likely than women to use both alcohol and tobacco (27.5 vs. 16.4 percent, respectively), whereas women were more likely than men to abstain from both substances (34.9 vs. 21.8percent, respectively).Prevalence by Age-Group.The preva lence of alcohol use by age-group showed a somewhat curvilinear pattern for both men and women (Figure 1b).Alcohol use was common among people ages 18-24 (74.8 and 66.8 percent for men and women, respectively), peaked at ages 25-44 (77.7 and 68.3 percent, respectively), began to decline among people ages 45-64 (70.4 and 58.5 per cent, respectively), and was lowest among people ages 65 and older (55.4 and 37.6 percent, respectively).

Prevalence of Alcohol and Tobacco Use and Co-Use
In contrast, tobacco use declined monotonically for both genders, with the highest prevalence among the youngest group (38.6 and 28.4 percent for men and women, respectively) and the lowest prevalence among the oldest group (18.2 and 10.4 percent, respec tively).Similarly, the prevalence of co use of alcohol and tobacco declined steadily with age, from the highest rate among people ages 18-24 (34.8 and 25.5 percent for men and women, respectively) to the lowest rate among people ages 65 and older (11.3 and 4.6 percent, respectively).
Prevalence by Race/Ethnicity.The prevalence of alcohol use varied among racial/ethnic groups for both men and women.For both genders, Whites displayed the highest rates (74.3 and 65.1 percent for men and women, respectively) and Asians/Native Hawaiians/ Pacific Islanders displayed the lowest rates (61.5 and 36.1 percent, respec tively) (Figure 1c).The prevalence of tobacco use for both genders was high est among American Indians/Alaskan Natives (49.6 and 34.1 percent for men and women, respectively) and lowest among Asians/Native Hawaiians/ Pacific Islanders (22.2 and 8.9 percent, respectively).Parallel to this pattern, the prevalence of using both alcohol and tobacco was highest among American Indians/Alaskan Natives (34.0 percent among men and 22.8 percent among women) and Asians/Native Hawaiians/ Pacific Islanders had the lowest prevalence (18.1 and 6.6 percent, respectively).Whites, Blacks, and Hispanics had intermediate levels of co-use.

Prevalence of AUDs, Nicotine Dependence, and Comorbidity
NESARC provides national prevalence estimates of AUDs, nicotine depen dence, and their comorbidity, by age and race/ethnicity for men and women separately.According to these data, 8.4 percent of adults in the United States had an AUD and 12.8 percent had nicotine dependence during the past year (Table 2, Figure 2a).Moreover, 2.9 percent of all adults had a comor bid AUD and nicotine dependence, representing approximately 6.2 million adults.Additional analysis found that the prevalence of comorbid alcohol and nicotine dependence was slightly higher than the prevalence of comorbid alcohol abuse and nicotine dependence (1.7 vs. 1.2 percent, respectively) (Figure 2a).Although men and women had similar rates of nicotine dependence only (10.0 and 9.7 percent, respectively), men were more likely than women to have an AUD only (8.2 vs. 3.1 percent, respectively) and comorbid disorders (4.1 vs. 1.8 percent, respectively).
Prevalence by Age-Group.For both genders, the prevalence of AUDs, nico tine dependence, and comorbid disor ders decreased with age (Figure 2b).The prevalence of AUDs was highest among the youngest men and women (25.1 and 11.7 percent, respectively) and lowest among the oldest men and women (2.8 and 0.5 percent, respec tively).Similarly, the prevalence of nicotine dependence was highest among the youngest men and women (19.1 and 15.2 percent, respectively) and lowest among the oldest men and women (4.6 and 3.7 percent, respec tively).For each age-group, nicotine dependence generally was more preva lent than AUDs, except for men ages 18-24, for whom AUDs were more prevalent than nicotine dependence (25.1 vs. 19.1 percent, respectively).Like the rates of AUDs and nicotine dependence, the prevalence of comor bid disorders decreased with age, with the highest prevalence found among the youngest men and women (9.9 and 4.7 percent, respectively) and the low est prevalence found among the oldest men and women (0.4 and 0.1 percent, respectively).Finally, for all diagnoses and age-groups evaluated, prevalence of AUDs and/or nicotine dependence was higher among men than among women.Prevalence by Race/Ethnicity.For AUDs, American Indians/Alaskan Natives displayed the highest preva lence (15.9 and 8.7 percent for men and women, respectively) and Asians/ Native Hawaiians/Pacific Islanders had the lowest rates (6.8 and 2.5 percent, respectively) (Figure 2c).The preva lence of nicotine dependence showed greater variability among the racial/eth nic groups.For both men and women, the highest rates were found among American Indians/Alaskan Natives (26.4 and 20.2 percent, respectively).Among men, Hispanics had the lowest rate (7.0 percent), whereas among women, Asians/Native Hawaiians/ Pacific Islanders had the lowest rate (4.5 percent).Across all racial/ethnic groups, the prevalence of nicotine dependence generally was greater than the prevalence of AUDs with the exception of Hispanic men, in whom the prevalence of AUDs (12.1 percent) exceeded that of nicotine dependence (7.0 percent).For comorbid AUDs and nicotine dependence, the rank ordering pattern among the racial/ethnic groups was similar for both genders: American Indians/Alaskan Natives displayed the highest prevalence (7.0 and 4.0 percent for men and women, respectively) and Hispanics had the lowest rates (2.2 and 0.9 percent, respectively).

Prevalence of Tobacco Use, Daily Tobacco Use, and Nicotine Dependence by Drinking Characteristics
NESARC data also demonstrate how tobacco use is related with the characteris tics of alcohol consumption.For all three tobacco measures-that is, tobacco use, daily tobacco use, and nicotine depen dence-the rates increased monotonically with increasing levels of alcohol con sumption and the presence of alcohol abuse and dependence (Table 3, Figures 3A-C).For instance, among both men and women, the prevalence of tobacco use was lowest among lifetime alcohol abstainers (12.7 and 8.0 per cent, respectively), increased with levels of alcohol consumption, and peaked among alcohol-dependent individuals (66.3 and 59.7 percent, respectively) (Figure 3A).Similar positive trends also were observed between drinking charac teristics and daily tobacco use (Figure 3B) or nicotine dependence (Figure 3C).The association between alcohol depen dence and nicotine dependence was particularly strong.Compared with the prevalence of nicotine dependence among male and female lifetime alcohol abstainers (3.8 and 2.9 percent, respectively), the prevalence of nicotine dependence among alcohol-dependent men and women was much higher (44.6 and 47.3 percent, respectively), representing an 11.7 and 16.3 times increased risk for nicotine dependence, respectively.

Discussion and Conclusion
This study presents updated epidemio logic data on alcohol and tobacco co-use and comorbidity in the adult population of the United States.With approxi mately 46.2 million American adults having used both substances in the past year, the sheer extent of co-use is high.
The number for comorbid disorders is considerably lower, yet still significant, with approximately 6.2 million American adults having both an AUD and nicotine dependence.Furthermore, higher rates of co-use and comorbidity were found among certain demographic subgroups.For example, similar to Anthony and Echeagaray-Wagner (2000), the current analysis revealed that the prevalence of co-use and comorbidity was higher in men than women.Moreover, the highest rates were seen in the youngest age-groups, with a steady decline observed in older age-groups.Among the racial/ethnic subpopulations, American Indians/ Alaskan Natives had the highest rates of alcohol and tobacco co-use and comorbidity among both men and women.This last finding is particularly important, despite being rarely reported in the literature.Overall, the higher rates of co-use and comorbidity found in these demographic subgroups were not surprising, given reports in the literature of higher rates of alcohol use, tobacco use, AUDs, and nicotine dependence among these subpopulations (American Lung Association 2006;CDC 2005a;NIAAA 1998a,b).Results from the current study suggest that preven tion and treatment strategies for comorbid alcohol and tobacco use dis orders should place a special emphasis on men and focus efforts on other high-risk groups such as young adults and American Indians/Alaskan Natives.
In addition to quantifying the current rates of co-use and comorbidity in the United States, the present study also investigated the association between the characteristics of alcohol and tobacco use.Results showed a dose-response relation-   Soeken and Bausell (1989) showed a relatively linear increase in smoking rates in a national sample of adults ranging from 18 percent among abstainers to 27 and 38 percent among moderate and heavy drinkers, respectively.The differences in the estimated rates of smok ing among alcohol consumption groups in these studies may result from differ ing operational definitions of smoking and levels of alcohol consumption, the use of community versus national sam ples, and changing trends in surveys conducted in different years.The present study improves on a significant portion of the existing studies by including all modalities of tobacco use rather than focusing only on cigarette smoking.The rationale for including all modalities of tobacco use is that all modalities have been shown to have detrimental health consequences when used in excess (CDC 2004(CDC , 2005c)).For those wishing to draw comparisons to studies involving only cigarette smoking, it is noteworthy that separate analyses revealed that cigarette smoking accounted for approximately 88 percent of all tobacco use.Thus, the prevalence esti mates of alcohol and tobacco use and co-use presented in this study provide health care policymakers and treatment planners with a comprehensive assessment of the state of the use and dual-use prob lem in America.Nonetheless, the current study is descriptive in nature.Given the high rates of co-use and comorbidity in this country, continued research into the mechanisms underlying co-use and comorbidity certainly are warranted.■

Financial Disclosure
The authors declare that they have no competing financial interests.

Figure 1b
Figure 1b Prevalence (%) of past-year alcohol use, tobacco use, and co-use by age and gender in the United States, 2001-2002 NESARC.

Figure 1c
Figure 1c Prevalence of past-year alcohol use, tobacco use, and co-use by race/ethnicity and gender in the United States, 2001-2002 NESARC.NOTE: Data are drawn from Table 1.W = White; B = Black; AI/AN = American Indian/Alaskan Native; A/NH/PI = Asian/Native Hawaiian/Pacific Islander; H = Hispanic.

Figure 2a
Figure 2a Prevalence of past-year alcohol use disorder, nicotine dependence, and comorbid disorders in the United States, 2001-2002 NESARC.NOTE 1: Data are drawn from Table 2. ND = nicotine dependence; AUD = alcohol use disorder; AD = alcohol dependence; AA = alcohol abuse.NOTE 2: The prevalence of AUDs or ND only is derived as follows: % AUD only = % AUD -% comorbid; % ND only = % ND -% comorbid.

Figure 2b Figure 2c
Figure 2b Prevalence (%) of any past-year alcohol use disorder, nicotine depen dence, and comorbid disorders by age and gender in the United States, 2001-2002 NESARC.NOTE 1: Data are drawn from Table 2. AUD = alcohol use disorder; ND = nicotine dependence.NOTE 2: The prevalence of AUD or ND only is derived as follows: % AUD only = % AUD -% comorbid; % ND only = % ND -% comorbid.

Figure 3 AB
Figure 3 A Prevalence of past-year tobacco use by past-year drinking character istics and gender in the United States, 2001-2002 NESARC.B Prevalence of past-year daily tobacco use by past-year drinking char acteristics and gender in the United States, 2001-2002 NESARC.C Prevalence of past-year nicotine dependence by past-year drinking characteristics and gender in the United States, 2001-2002 NESARC.

Table 1
Prevalence (%) of Past-Year Alcohol and Tobacco Use and Co-Use in the United States, By Gender, Age, and Race/Ethnicity, 2001-2002 NESARC Figure 1a Prevalence of past-year alcohol and tobacco use and co-use in the United States, 2001-2002 NESARC.
SE = standard error of the estimated percentage.NOTE: Data are drawn from Table1.The prevalence of alcohol or tobacco use only is derived as follows: % alcohol use only = % alcohol use -% co-use; % tobacco use only = % tobacco use -% co-use.

Table 2
Prevalence (%) of Past-Year Alcohol Use Disorders, Nicotine Dependence, and Comorbid Disorders in the United States, by Gender, Age, and Race/Ethnicity, 2001-2002 NESARC

Table 3
Prevalence (%) of Past-Year Tobacco Use, Daily Tobacco Use, and Nicotine Dependence by Drinking Characteristics and Alcohol Use Disorders in the United States, 2001-2002 NESARC NOTE: SE = standard error of the estimated percentage; AUD = alcohol use disorder.